Doctor Victor Frankenstein and his infamous monster are some how sent to Equesrtia of all places. The mad doctor has little choice but to side with his monster to find a way out and not be discovered at the same time. If the doctor cannot get them out they may be discovered and then he fears the residents may cause major problems for him and his monster.
spoiler warning: if you haven't read the book, first I recommend it, and second the book and the movies don't share that much in common so be prepared to not understand me alluding to the book